Internal defects and diagnostic methods of power transformers

As one of the key devices in the power system, power transformers are responsible for adjusting voltage levels to meet the needs of power transmission and distribution. However, during long-term operation, power transformers may experience various faults and internal defects, which have a serious impact on the safety and stability of the power system. Therefore, timely detection and diagnosis of internal defects in transformers are important means to maintain the normal operation of the power system.

The internal defects of power transformers mainly include winding partial discharge, aging of insulation materials, short circuit, open circuit and grounding. Winding partial discharge refers to the discharge phenomenon caused by the electric field strength of the insulating material inside the winding exceeding its voltage resistance capability. This discharge will not only damage the insulating material, but also produce high-frequency noise and electromagnetic interference, affecting the normal operation of the system. Winding insulation aging is due to the aging and degradation of insulation materials caused by long-term operation and overload, resulting in a decrease in the insulation capacity of the winding. A short circuit refers to the occurrence of a DC or AC low-impedance path inside the transformer winding, resulting in an abnormal increase in current. Open circuit refers to the internal circuit breakage of the transformer winding, making it impossible to transmit electrical energy. Grounding is when insulation failure within a transformer winding results in a direct short circuit between the winding and ground.

In order to promptly discover and diagnose internal defects of transformers, people often use various methods for detection and monitoring. Among them, one of the most commonly used methods is winding partial discharge detection. Winding partial discharge detection is to determine whether there is discharge in the transformer winding through the capture and analysis of discharge signals. It is usually carried out using technical means such as high-frequency detection method, ultrasonic detection method and infrared thermal imaging detection method. The high-frequency detection method uses high-frequency voltage to excite the winding and detects the high-frequency current signal inside the winding to determine the partial discharge phenomenon. The ultrasonic detection method uses the scattering and attenuation characteristics of ultrasonic waves to detect the partial discharge sound inside the winding. The infrared thermal imaging detection method is to determine whether there are hot spots and partial discharges inside the winding by recording the temperature distribution on the winding surface.

In addition to winding partial discharge detection, diagnosis of insulation material aging and short circuit is also one of the important methods for diagnosing internal defects of transformers. The aging of insulation materials is generally evaluated by measuring the resistance and capacitance of the windings. Resistance measurement is to determine whether there is insulation aging or insulation damage in the winding by measuring the resistance value between two points of the winding. Capacitance measurement determines the insulation quality of the winding by measuring the capacitance of the winding. If there is a short circuit, you can determine whether there is a short circuit in the winding by measuring the insulation resistance and voltage drop of the winding.

In addition, the detection of open circuits and grounding is also an important method for timely discovery and diagnosis of internal defects in transformers. Open circuit can be judged by measuring the insulation resistance and capacitance of the winding to determine whether there is an open circuit in the winding. For grounding, you can determine whether the winding is grounded by measuring the resistance and potential difference between the winding and the ground. These measurements can be made using equipment such as multimeters, insulation resistance meters, and ground resistance meters.

In summary, internal defects of power transformers have a serious impact on the normal operation of the power system. Therefore, timely detection and diagnosis of internal defects of the transformer are necessary to maintain the safe and stable operation of the power system. Methods such as winding partial discharge detection, insulation material aging and short circuit diagnosis, open circuit and grounding detection can effectively discover and diagnose internal defects of the transformer. With the continuous advancement of science and technology, these methods are also constantly developing and innovating, providing more accurate and reliable means for diagnosing internal defects in transformers.